I run sound for a pretty large church, with a pretty large choir, and a pretty lively service, and we now do it successfully each Sunday. It hasn't been without some gnashing of teeth, some equipment changes, so I'll tell you what we do and what we use. First off, you never ever run the choir mics back through the choir monitors. Many will die, not an option. One of the first things I did was to change choir mics. We were using hanging condenser hyper-cardioid mics with limited success. They worked OK when we were a mostly traditional piano and organ church, but as we became more and more blended/contemporary, our old mics where showing their limitations. Our sanctuary has high ceilings and is fairly reverberant. The mic properties, coupled with the room characteristics and a loud stage were causing low choir volume and transient frequencies to be reproduced. We use Heil PR30's with great success. They are dynamic not condenser mics. They have pretty tight pick-up pattern, and being cardioid, they don't pick up sound from the rear like super and hyper mics do. They aren't as sensitive as condenser mics, but that's why we chose them. I use three microphones for a 60-70 member choir standing in three rows. Second was to make sure the stage around the choir was as quiet as it possibly could be. We switched the band from open monitors to ears and personal monitor mixers. Like someone said above, the loudest sound at the microphone is what you will hear. No way around that one, pure and simple physics. It also helps on how loud your choirs monitors have to be. I also moved loud acoustical instruments (piano/brass) to the front away from the choir. The new mics do a lot better on a loud stage (orchestra) but do even better when the stage volume is under control. At our church, our praise team are also members of the choir. They stand out front and sing with the choir and sing parts. Sometimes I have 8 singers with individual mics on stage along with a full choir behind them. Having a team singing the same thing and the same parts as the choir is a lifesaver. If you use them right, and assuming you have good singers, you can really make your choir number standout with clarity. You have to use your miked singers as your base. Just like mixing your band, you have a key instrument that you build off of. Put them in a console group, mix them, and slightly compress the group, and add a touch of reverb. Make them your base singers and them bring your choir mics up to build in around them. We have come a long way. I can honestly say, I'm happy with our sound right now. I haven't said that many times over the 20 years I've been doing this.